Metal oxide coated substrates

ABSTRACT

Multilayered metal oxide coated substrates are disclosed comprising a three dimensional inorganic substrate having a coating of metal oxide on at least a portion of all three dimensions thereof, produced by a unique process having particular applicability to the manufacture of tin oxide coated three dimensional substrates. Certain novel coated substrates, such as flakes, spheres and porous substrates are disclosed. The coated substrates are useful in polymers, catalysis, heating and shielding applications.

BACKGROUND OF THE INVENTION

The present invention relates to a process for coating particlesubstrates, the coated particle substrate and to applications and usesthereof. More particularly, the invention relates to coating particlesubstrates with a metal oxide-containing material, such materialpreferably being an electrically conductive and/or ferromagneticoxide-containing material and such coated substrate.

In many electronic and/or ferromagnetic applications it would beadvantageous to have an electrically, electronically conductive; electromechanical and/or ferromagnetic metal oxide coating which issubstantially uniform, has high and/or designed electronic conductivity,and/or ferro magnetic properties and has good chemical properties, e.g.,morphology, stability, etc.

A number of techniques have been employed to provide certain metal oxidecoatings on substrates. The CVD process is well known in the art forcoating a single flat surface, which is maintained in a fixed positionduring the contacting step. The conventional CVD process is an exampleof a “line-of-sight” process or a “two dimensional” process in which themetal oxide is formed only on that portion of the substrate directly inthe path of the metal source as metal oxide is formed on the substrate.Portions of the substrate, particularly internal surfaces, which areshielded from the metal oxide being formed, e.g., such as the oppositeside and edges of the substrate, pores or channels which extend inwardlyfrom the external surface and substrate layers which are internal or atleast partially shielded from the depositing metal oxide source by oneor more other layers or surfaces closer to the external substratesurface being coated, do not get uniformly coated, if at all, in a“line-of-sight” process. Such shielded substrate portions either are notbeing contacted by the metal source during line-of-sight processing orare being contacted, if at all, not uniformly by the metal source duringline-of-sight processing. A particular problem with “line-of-sight”processes is the need to maintain a fixed distance between the sourceand the substrate. Otherwise, metal oxide can be deposited or formed offthe substrate and lost, with a corresponding loss in process and reagentefficiency.

In an attempt to overcome the limitations of the “line-of-sight”processes it has been proposed to contact a three dimensional substratewith a metal oxide precursor wherein the precursor preferably forms aliquidous metal oxide precursor on the substrate. The formed coatedsubstrate is subjected to oxidation conditions to convert the metaloxide precursor to the metal oxide coated substrate (U.S. Pat. No.5,326,633 [1994], U.S. Pat. No. 5,603,983 [1997], U.S. Pat. No.5,633,081 [1997] and U.S. Pat. No. 5,756,207 [1998] granted to Clough etal.) While these processes represent a significant advance over theprior art CVD “line-of-sight” processes described above, the Clough etal. processes typically require total times for contacting,equilibration and oxidation in the range of minutes to hours.

It has been desirable to further improve the processes for producingmetal oxide coated substrate particles particularly under fast reactionprocessing conditions which significantly reduce the processing timesrequired for producing metal oxide coated particle substrates and toproduce unique metal oxide coated substrates having improved properties

BRIEF SUMMARY OF THE INVENTION

A new process, e.g., a “non-line-of-sight” or “three dimensional”process, useful for coating of three dimensional particle substrates hasbeen discovered. As used herein, a “non-line-of-sight” or “threedimensional” process is a process which coats surfaces of a substratewith a metal oxide coating which surfaces would not be directly exposedto metal oxide-forming compounds being deposited on the external surfaceof the substrate during the first line-of-sight contacting step. Inother words, a “three dimensional” process coats coatable substratesurfaces which are at least partially shielded by other portions of thesubstrate which are closer to the external surface of the substrateand/or which are further from the metal oxide forming source duringprocessing, e.g., the internal and/or opposite side surfaces of forexample glass, ceramic or mineral particle substrates such as fibers,spheres, flakes or other shapes or surfaces including porous shapes.

A new fast reaction, elevated temperature process for at least partiallycoating a three dimensional substrate having shielded surfaces with ametal oxide, preferably an electrically conductive or ferromagneticmetal oxide coating on at least a part of all three dimensions thereofand on at least a part of said shielded surfaces thereof has beendiscovered. In brief, the process comprises contacting the substrateparticles with a metal oxide precursor, for example, stannous chloride,stannic chloride, stannous oxide, zinc chloride, cuprous chloride,ferric chloride or titanium tetrachloride in a liquid form and/or in asolid form, to form a metal oxide precursor/substrate reactant mixture;preferably contacting the substrate also with at least one interactingcomponent, i.e., a conductivity interactive or a ferromagneticinteracting component and contacting the reactant mixture with anoxidizing agent under fast reaction short residence time, highertemperature condition to form a metal oxide coated substrate andrecovering such coated substrate, preferably a semi conductor orferromagnetic oxide-containing coated substrate more preferably ann-type oxide semi conductor, more particularly a doped semi-conductorand/or semi conductor having a defect and/or non-stoichiometricstructure which enhances conductivity. The contacting of the substratewith the metal oxide precursor and optionally with the interactingcomponent to form the reactant mixture takes place prior tosubstantially deleterious oxidation of the metal oxide precursor. In aparticularly preferred embodiment, the reaction mixture is introduceddirectly into a high temperature oxidizing reaction zone under fastreaction processing conditions. The coated substrate is then recoveredby conventional means.

The process can provide unique coated substrates including single andmixed oxides which have application designed electrical conductivity ormagnetic properties and/or pearlescent or transparent properties so asto be suitable for use as components such as additives in a wide varietyof applications. Substantial coating uniformity, e.g., in the thicknessof the metal oxide coating and in the distribution of interactingcomponent in the coating, is obtained. Further, the present metal oxidecoated substrates in general have outstanding stability, e.g., in termsof electrical or magnetic properties and morphology and are thus usefulin various applications.

DETAILED DESCRIPTION OF THE INVENTION

The present coating process comprises forming a reactant mixture bycontacting a substrate with a metal oxide precursor, such as metalchloride forming components, metal complexes and mixtures thereof andcontacting the reactant mixture with an oxidizing agent, at fastreaction, elevated temperature process conditions, preferably oxidizingand hydrolyzing conditions, effective to form a metal oxide containingcoating on the substrate. The reactant mixture preferably comprises atleast one conductivity or magnetic interacting component, hereinafterreferred to as interacting or interactant component, such as at leastone dopant compound, in an effective amount to form an interactingcomponent-containing coating, such as a dopant component-containingcoating, on at least a portion of the substrate. The reactant mixture,preferably with an interacting component, for example a dopantcomponent, are contacted with at least one oxidizing agent at conditionseffective to convert the metal oxide precursor to metal oxide and form ametal oxide-containing coating, preferably a semi conductor, or magneticmetal oxide-containing coating, on at least a portion of the substrate.The process as set forth below will be described in many instances withreference to various compounds of stannous chloride, stannic chloride,zinc chloride, stannous oxide, cuprous chloride, titanium chloride, andferric chloride which have been found to provide particularlyoutstanding process and product properties. However, it is to beunderstood that other suitable oxide precursors are included within thescope of the present invention.

As set forth above the reactant mixture is subjected to oxidizing fastreaction processing conditions at elevated temperatures in order to forma metal oxide coating on the substrate. The reactant mixture should beformed prior to deleterious oxidation of the metal oxide precursor i.e.nondeleterious oxidation. This could result in oxidation of the metaloxide precursor off of the substrate thereby decreasing the yield ofmetal oxide coated substrate. By “non-deleterious oxidation” is meantthat the metal oxide precursor, for example stannous chloride, zincchloride, cuprous chloride and ferric chloride is associated with thesubstrate before deleterious oxidation of the metal oxide precursortakes place off the substrate, such as not to be associated with thesubstrate coatings. It has been found that the preferred reactantmixtures are those that are formed prior to the introduction of thereactant mixture into the high temperature fast reaction zone. Thus forexample, the reactant mixture can be a liquid slurry wherein the metaloxide precursor is soluble in the liquid optionally with the interactantbeing soluble and/or solid in the liquid slurry. Further, the liquidslurry can be a suspension of the metal oxide precursor with thesubstrate preferably as a precipitate on the substrate in the liquidsolid slurry. Further the reactant mixture can be a solid or powder suchas a metal oxide precursor coated substrate. Each of the above reactantmixtures can offer unique and distinct processing product advantages inthe process of this invention. The liquid part of the reactant mixturesis preferably atomized, such as gas atomized, upon introduction with thesubstrate into the reaction zone for oxidation to the metal oxidesubstrates. Further, the solid reactant mixtures such as powdermixtures, can be air fluidized into the reaction zone or gravity ormechanically fed into the reaction zone. For the liquid reactantmixtures, it is preferred to maximize the concentration of the substratein the liquid slurries on a wt% basis so as to maximize the associationof the metal oxide precursor and optionally interacting component withthe substrate. It is preferred that the concentration of substrate inliquid slurries be from about 10 to 60 wt% more preferably from about 30to 50 wt% or higher. As is recognized by those of skill in the art, theviscosity of the slurries will vary as a function of both the particlesize, its geometry and density. Viscosities are used which allow foroverall optimum process efficiencies on a product quality and throughputbasis.

The fast reaction processing conditions as set forth above include avery short oxidation reaction residence time for the particle in theelevated temperature reaction zone. “Reaction zone” is defined as thatzone at elevated temperature wherein fast oxidation of the metal oxideprecursor takes place on the substrate such that the metal oxideprecursor is not substantially lost as separate metal oxide particlesnot associated with the substrate. Thus the reaction zone allows forassociation of the metal oxide precursor on the substrate whereinsubsequent processing will not substantially adversely affect theoverall metal oxide coating on the substrate. It is important that theresidence time in the elevated temperature reaction zone associate themetal oxide precursor with the substrate. It is contemplated within thescope of this invention that further processing such as sintering orcalcination to promote further oxidation uniform crystalinity and/orcoating densification can be carried out according to the process ofthis invention.

The fast reaction processing conditions in the oxidation reaction zonecan vary as to temperature and residence time according to the physicaland chemical properties of the metal oxide precursor, interactingcomponent and substrate. The average particle residence time in theoxidizing reaction zone is from about 1 millisecond to about 1 second,more preferably from about 2 milliseconds to 500 milliseconds and stillmore preferably from about 10 milliseconds to 250 milliseconds. Further,the residence time can be defined by the particle velocity in thereaction oxidizing zone. Preferably the average particle velocity in thereaction zone is from about three to about 30 meters/second, morepreferably from about three to about 10 meters/second.

The elevated temperature in the reaction zone is maintained by a thermalsource that rapidly transfers thermal energy to the reactant mixture.The unique combination of reactant mixture, short residence time and athermal source for rapid thermal transfer provides for rapid associationof the metal oxide precursor with the substrate on both external andshielded surfaces without substantially adversely effecting the solidintegrity of the substrate. By the term solid integrity is meant thatthe substrate retains at least a part preferably a majority an even morepreferably a substantial majority of the substrate as a solid under thetemperature conditions in the reaction zone. Depending on the physicaland chemical properties of the substrate the surface and near surface ofthe substrate can melt under the thermal conditions in the reactionzones. The rapid melting and solidification for certain substrates canprovide enhanced properties associated with the metal oxide coating suchas barrier properties, binding properties and preferential crystallinesurface formation by the substrate. The short residence times in thereaction zones allow for rapid chemical reactions and rapid quench whenthe substrate particles leave the reaction zone.

The thermal source produces elevated temperatures that allow for thereactant mixture to rapidly produce metal oxide coated substrates andallows residence times that provide for the association of the metaloxide precursor with the substrate. Thus the thermal source must allowfor control of the elevated temperature to produce metal oxide coatedsubstrates and a residence time which allows the chemical reactionsand/or association of the metal oxide precursor with the substrate totake place on the substrate. The preferred thermal sources which allowfor control of elevated temperatures and the residence times necessaryfor chemical reaction and/or association of the metal oxide precursorwith the substrate are induction plasma sources preferably RF inductionplasma sources and flame combustion sources.

As set forth above, the thermal source provides an elevated temperaturethat primarily acts on the metal oxide precursors and optionallyinteractants and added components to the liquid slurry or powders suchthat the substrate, primarily the internal portions of the substrate areat a lower temperature than the external temperature in the reactionzone. As will be more fully described below, the typical substrate canhave a relatively low heat transfer coefficient which when combined withthe residence times in the reaction zone allows for such differentialbetween the external temperature and the internal temperature of thesubstrate. Further the processing conditions can be adjusted to takeadvantage of this thermal gradient particularly as to selective melt andresolidification and crystallization on the surface and near surface ofthe substrate. Further, the temperature within the reaction zone iscontrolled to allow rapid oxidation and/or hydrolysis of the metal oxideprecursors and/or interacting component which reactions can increasesubstantially the association of the coating i.e. reduced tendencytowards volatilization, the completion of the overall oxidation reactionto metal oxide coating. As set forth above, one of the major advances isthe association of the metal oxide precursor coating through thereaction zone into the quench stage. The recovered metal oxide coatedsubstrates can be further calcined, sintered or annealed for oxidation,densification and crystallization.

RF inductively coupled plasma systems are well known to those ofordinary skill in the art and typically consist of an RF power generatorsupplying a RF current to an induction coil wound around a plasmaconfinement tube. The tube confines the plasma discharge. Power levelsfor plasma systems can vary from about 10 kW up to about 500 kW. Typicalfrequencies vary from about 0.3 MHz to even as high as 14 MHz. Typicalranges are in the 0.3 to 5 range.

The plasma system typically uses three different gases including acentral gas sometimes referred to as a central swirl gas used primarilyfor formation of the plasma, a sheath gas used primarily to stabilizeand center the plasma and a third carrier gas which typically is used totransport a powder feed and/or atomize a liquid or liquid slurry feed.As is recognized by those of ordinary skill in the art, the compositionof all three gases can vary and can include gases such as argon,nitrogen, hydrogen and other gases such as oxygen, carbon dioxide,carbon monoxide and water. In addition mixtures of varying gases can beused depending on the characteristics of the plasma that is required forthe process. As set forth above, a component of the plasma gases canserve as the oxidizing agent. In other cases, a secondary gas can beinjected into the plasma or sheath surrounding the plasma to provide theoxidizing agent. For example, water vapor can be used as a secondary gasto promote the overall oxidation hydrolysis of the metal oxide precursorto metal oxide coating. Further, as set forth above, the presence ofwater vapor enhances formation of crystalline metal oxide coatingshaving improved conductivity and/or magnetic properties. The gases usedas sheath, central and carrier gases can be different or the same andmixtures of different gases can be used. For example, air can be usedfor the sheath, central and carrier gas or various other gases, such asargon, can be combined with the sheath or central gas. The gas flowrates for the central, sheath and carrier gases can vary over a widerange with such ranges being adjusted to within the residence time andparticle velocities required for the conversion of the metal oxideprecursor to coated metal oxide substrate. In general the rate ofintroduction of the sheath, central and carrier gases will vary withtypically the sheath gas being introduced at a rate of from about threeto about five times that of the central swirl gas. In addition, thecentral swirl gas rate will generally be higher than the carrier gassince the carrier gas is used to control the rate at which the reactantmixture is introduced into the reaction zone. The gas compositions andflow rates can be optimized to provide desired process conditions. Forexample, nitrogen can be introduced into the central gas in order tolower the overall temperature profile within the reaction zone.Typically the other gas rates and/or partial pressure within the givengas composition are lowered in order to control the particle residencetime and particle velocities within the reaction zone. Further, theoxygen content in the various gases within the reaction zone can beadjusted to provide near stochiometric quantities of oxygen or slightexcess in order to limit the oxygen present in the later portion andtail of the reaction zone. In addition, oxygen enrichment can take placesuch as the introduction of oxygen, such as air, at the tail of thereaction zone to provide enhanced overall oxidation conditions prior toquench. Typically, the enthalpy of the gas composition is controlled soas to maintain the elevated temperature that promotes rapid oxidationand/or hydrolysis of the metal oxide precursors on the substrate. Thusthe enthalpy of components such as hydrogen and organic components addedas part of the liquid slurry and powder reaction mixtures are taken intoconsideration for defining the temperature required in the reactionzone. Further, the gas rates (volume of gas per unit time) will varydepending on the size and design of the process equipment. As set forthabove, the residence times are long and the particle velocities slowwhen compared to typical sonic and supersonic plasma type systems. As isset forth above, an oxidizing agent, preferably oxygen preferably asoxygen in air or decomposition of water vapor, allows for the oxidationreaction of metal oxide precursor to metal oxide coating on thesubstrate to take place within the reaction zone at elevatedtemperatures. It has been found that the residence times and/or particlevelocities as set forth above together with the control of gascomposition and temperature conditions allow for the oxidation reactionsto take place on the substrate to produce the metal oxide coatedsubstrates. The control by the thermal source of the temperature in theplasma or adjacent to the plasma, i.e. reaction zone, allows for theoxidation reactions to take place while not substantially adverselyeffecting the solid integrity of the substrate. Further, the temperatureand the dimension of the plasma can be adjusted so as to provideselective melting on the surface or near surface of the substrate toenhance overall bonding and uniformity of the metal oxide coating on thesubstrate. As set forth above, the temperature, particle residence timeand oxidizing agent concentration allow for the oxidation of the metaloxide precursor to metal oxide coating while not adversely effecting thesolid integrity of the substrate. Thus, the temperature within thereaction zone can vary according to the above process conditions andtypically are in the range of from about 1000° K. to about 4000° K.,more preferably up to about 3000° K. As set forth above, the temperaturecan be moderated by auxiliary gases including inert gases and watervapor.

The reactant mixture can be introduced into the plasma at varyinglocations within the plasma including the tail, i.e. terminal, portionof the plasma flame. The reactant mixture in addition can be introducedlaterally into or adjacent to the plasma flame and/or the tail of theplasma flame or at varying angles to the plasma including perpendicularto the plasma or the plasma tail. In a typical system configuration aprobe of appropriate metallurgy such as inconel in the presence offluorides, is centrally mounted in the plasma confinement tube.Typically a quartz tube is interposed between the probe and theconfinement tube. The central gas in injected into the quartz tube andthe sheath gas is injected in the annular passage defined between thequartz tube and the plasma confinement tube. Conventional cooling of thesystem is used. The reactant mixture feed probe can be used to gasatomize the liquid slurry reaction mixtures of this invention and/or gasatomize, such as with air, the powder feeds of this invention. Forexample, in the liquid slurries, fine droplets of the liquid slurriescan be injected typically into the central portion of or adjacent to theplasma discharge. Further, the position of the injection probe within oradjacent to the plasma for powder or liquid slurries can be varied suchas to optimize the performance and overall yields of metal oxide coatedsubstrates. As is set forth above, the reaction mixture can beintroduced into the tail of the plasma discharge such as laterally or atan angle into the plasma tail. It is preferred that the reactantmixtures from liquid slurries to powders be introduced into the reactionzone with a carrier gas, particularly an oxygen containing carrier gaswhich enhances the rate of oxidation of the metal oxide precursor tometal oxide coating on the substrate. The powders can be gravity fedand/or continuously fed such as by screw feeders into the plasma. In apreferred embodiment of this invention, the concentration of thesubstrate in the liquid slurries can be maintained at a relatively highconcentration such as from 30 to 50-wt % or higher in order to optimizethe interaction between the metal oxide precursor, interacting componentand substrate. The concentration can be adjusted in order to maintain aliquid reactant mixture viscosity which enhances atomization of theliquid reactant mixture and overall steady state process and plasmaconditions for conversion and yield of metal oxide coated substrate.Further, the reaction zone can be run at varying pressures includingreduced pressures through higher pressures above atmospheric. The choiceof pressure is generally a function of the characteristics of the metaloxide precursor and interactant. It is preferred to maintain suchconditions of pressure which improve the overall conversion and yield ofmetal oxide coating on the substrate while reducing and/or minimizingthe reaction of metal oxide precursor to metal oxide off of thesubstrate.

The feed rates of the liquid slurries and powders in general are afunction of the reaction zone design and size. In general for smallscale reaction zone designs a feed rate of from 100 grams to 500 gramsper hour can be used, whereas for larger scale a feed rate of from 0.5Kg to 50 Kg per hour can be used.

The liquid slurries and powder mixtures can contain varioussubstantially nondeleterious materials including oxidizable materialssuch as solvents, i.e. alcohols for liquid slurries and organicpolymeric binders which can increase the elevated temperature orenthalpy in the reaction zone. The thermal contribution of theseoxidizable materials is used in order to design the thermal profile inthe reaction zone in order to maximize steady state process conditionsand conversion and yields of metal oxide coated substrate. Further, theuse of such oxidizable materials, particularly, organic materials can beused to adjust the composition of the plasma gases as a function of thegas composition from gas entry to exit from the reaction zone. Forexample, the oxygen requirement for oxidation of the metal oxideprecursor to metal oxide coating can be adjusted such that a portion ofthe plasma and gas composition exiting the tail of the plasma can be inan overall reducing environment. The process flexibility in theintroduction of varying gases of varying oxidizing and thermalcharacteristics allows such changes in gas composition as a function ofplasma profile and exit gases to be made. For example, in the use ofzinc oxide precursors, optionally with an interacting component such asan aluminum source, it has been found that the change from an oxidizingto a reducing environment enhances overall conductivity of the zincoxide film on the substrate. Further, the use of carbon dioxide such asin low oxygen containing gases from partial combustion of hydrocarboncan be used advantageously to promote the formation of a multipleoxidation and reduction zone within the reaction zones and/or areduction zone following the exit of the plasma gas from the reactionzone. Further, it is possible to add auxiliary gases such as reducinggases into the plasma at different introduction points within theplasma.

As set forth above, it is preferred that water in vapor form be part ofone of the gases used in the plasma reaction zone. It has been foundthat the water along with oxygen enhances the overall conversion ofmetal oxide precursor to metal oxide coating particularly the formationof the crystalline networks, which optimize the conductivity of themetal oxide coating. The water typically is present in the reactionmixture liquid slurries and/or is added as part of the central and/orsheath gases used in the formation of a stable plasma. The advantage ofthe presence of water vapor is the enhancement in the formation of theplasma as well as in enhancing the overall reactivity and oxidation ofthe metal oxide precursor to metal oxide coating.

The metal oxide coated substrates exit the reaction zone and are rapidlyquenched to lower temperatures including temperatures wherein relativelymoderate to low or even no significant oxidation is taking place of themetal oxide precursor. The metal oxide coated substrates are recoveredby conventional means such as typical powder particle collection means.As set forth above, the metal oxide coated substrates can be furtherprocessed such as by sintering and/or calcinations and/or annealing tofurther oxidize and/or densify the metal oxide coatings and/or morefully develop the optimum crystal structure for enhancing overallconductivity and/or magnetic properties of the final coated substrate.

As set forth above, the thermal source can be obtained from combustionsuch as a flame produced by the combustion of a flammable gas such asactylene, propane or low molecular weight hydrocarbons, such askerosene. The thermal and kinetic energy associated with the flamecombustion process can be varied to provide elevated temperatures andresidence times and/or particle substrate velocity within the ranges asset forth above. The combustion flame process provides a reaction zonewherein the gas composition within the reaction zone can be variedaccording to the gas combustion characteristics used to provide thereaction zone. Further, the composition of the gas can be variedaccording to the type of flammable gas used in the combustion processand the ratio of oxygen to inert gas that is used as the oxidant. Thusthe ratio of residual oxygen, carbon dioxide and water vapor can beadjusted by varying the stochiometry of the reactants and the type offuel source. Further, auxiliary gases can be added such as water vaporto moderate and modify the combustion flame characteristics. Inaddition, such auxiliary gases including inert gases can be addeddirectly into the combustion flame or as a sheath, i.e. curtain orshroud, surrounding the combustion flame. Further, the reactant mixturecan be introduced directly into the combustion flame or as in the caseof the RF induction plasma at varying angles to the flame or on theouter or adjacent surface or tail of the flame. The temperature profileswithin the combustion flame are typically lower than the temperaturesthat can be achieved in the RF induction plasma typically in the rangeof from about 750° K. to about 1,500° K. The unexpected processimprovement for producing metal oxide coated substrates with thecombustion flame is the formation of a reaction zone at temperatures andresidence times which allow for oxidation of the metal oxide precursoron the substrate. The various embodiments set forth above with respectto reaction mixture introduction into the reaction zone, preference foratomization of the reaction mixtures, variations on introduction of thereaction mixtures at various locations within the reaction zone or atthe tail end of the reaction zone, variations in gas composition such asoxidizing and reducing zones are applicable to the flame combustionprocess.

The thickness of the metal oxide-containing coating can vary over a widerange and optimized for a given application and is generally in therange of from about 0.01 to about 0.75 microns or even from about 0.03to about 0.5 microns, more preferably from about 0.05 micron to about0.25 microns, still more preferably from about 0.07 micron to about 0.2microns.

The reactant mixture may also include one or more other materials, e.g.,dopants, catalysts, grain growth inhibitors, binders, solvents, etc.,which do not substantially adversely affect the properties of the finalproduct, such as by leaving a detrimental residue or contaminant in thefinal product after formation of the metal oxide-containing coating.Thus, it has been found to be important, e.g., to obtaining a metaloxide coating with good structural, mechanical and/or electronic and/ormagnetic properties, that undue deleterious contamination of the coatingbe avoided. Examples of useful other materials include organiccomponents such as alcohols, i.e. methanol, ethanol, isopropanol andmixtures thereof, acetonitrile, ethyl acetate, dimethyl sulfoxide,propylene carbonate and mixtures thereof; certain inorganic salts andmixtures thereof. Certain of these other materials may often beconsidered as a carrier, e.g., solvent, for the metal chloride and/orinteracting component to be associated with the substrate to form thereactant mixture.

The metal oxide coatings are typically derived from transition metalprecursors, which contain transition elements of atomic numbers 21-31,39-49 and 71-81, inclusive and tin. Examples of such metals are tin,copper, zinc, iron, chromium, tungsten, titanium, molybdenum and indium.The preferred elements are tin, copper, zinc, iron, chromium, tungsten,titanium, molybdenum, indium and mixtures. The particularly preferredmetal elements are tin, zinc, iron, chromium, titanium and mixturesthereof.

As set forth above the metal oxide precursor is preferably selected fromthe group consisting of one or more metal chlorides, organic complexes,organic salts and oxidizable metal oxides such as stannous oxide. Forpowder reactant mixture it is preferred that metal chlorides, organiccomplexes and salts do not adversely oxidize and/or hydrolyze under theconditions of contacting the substrate with the metal oxide precursor toform the reactant mixture prior to oxidation to metal oxide in thereaction zone. Particularly preferred precursors are metal chlorides andlower valence oxidizable oxides and organic complexes, particularlydi-ketone type complexes, i.e., acetylacetonate complexes.

Typical examples of metal chloride precursors are stannous chloride,stannic chloride, cuprous chloride, zinc chloride, ferric chloride,tungsten pentachloride, tungsten hexa chloride, molybdenumpentachloride, indium dichloride, indium monochloride, chromium²chloride and titanium tetrachloride. Preferred metal complexes arepolyfunctional ketone complexes wherein such polyketone functionality iscapable of complexing with the metal. For example, acetylacetonatecomplexes, i.e., complexes of zinc, chromium and the like.

As set forth above, it has been found that the substrate can becontacted with a metal oxide precursor powder to form the reactantmixture. The metal oxide precursor powder can be applied to thesubstrate as a powder, particularly in the range of from about 1 toabout 10 microns in average particle size, the size in part being afunction of the substrate particle size, i.e. smaller substrateparticles generally require even smaller size powders. The powder ispreferably applied dry to a dry substrate and as a charged fluidizedpowder, in particular having a charge opposite that of the substrate orat a temperature where the powder contacts and adheres to the substrate.In carrying out the powder coating, a coating system can be, forexample, one or more electrostatic fluidized beds, spray systems havinga fluidized chamber, and other means for applying powder, preferably ina film forming amount. The amount of powder used is generally based onthe thickness of the desired metal oxide coating and incidental lossesthat may occur during processing. The powder process together withconversion to a metal oxide-containing coating can be repeated toachieve desired coating properties, such as desired gradientconductivities.

Typically, the fluidizing gaseous medium is selected to be compatiblewith the metal oxide precursor powder, i.e., to not substantiallyadversely affect the formation of a metal oxide coating on the substrateduring conversion to a metal oxide-containing film.

Generally, gases such as air, nitrogen, argon, helium and the like, canbe used, with air being a gas of choice, where no substantial adverseprehydrolysis or oxidation reaction of the powder precursor takes placeprior to the oxidation-reaction to the metal oxide coating. The gas flowrate is typically selected to obtain fluidization and charge transfer tothe powder. Fine powders require less gas flow for equivalentdeposition. It has been found that small amounts of water vapor enhancecharge transfer. The temperature for contacting the substrate with apowder precursor is generally in the range of about 0° C. to about 100°C. or higher, more preferably about 20° C. to about 40° C., and stillmore preferably about ambient temperature. The substrate however, can beat temperatures the same as, higher or substantially higher than thepowder.

The time for contacting the substrate with precursor powder is generallya function of the substrate bulk density, thickness, powder size and gasflow rate. The particular coating means is selected in part according tothe above criteria, particularly the geometry of the substrate. Forexample, particles, spheres, flakes, short fibers and other similarsubstrate, can be coated directly in a fluidized bed themselves withsuch substrates being in a fluidized motion or state. Typical contactingtime can vary from seconds to minutes, preferably in the range of about1 second to about 120 seconds, more preferably about 2 seconds to about30 seconds.

Typical metal oxide precursor powders are those that are powders atpowder/substrate contacting conditions and can be liquidous or solid atthe fast reaction process conditions at the elevated temperatures in thereaction zone. It is preferred that the powder at least partially meltsand substantially wets the surface of the substrate, preferably having alow contact angle formed by the liquid precursor in contact with thesubstrate and has a relatively low vapor pressure at the fast reactionand temperature conditions of oxidation, preferably melting within therange of about 100° C. to about 650° C. or higher. For tin oxideprecursor powder it is preferred that melting is within the range offrom about 100° to about 450°, more preferably about 250° C. to about400° C. As set forth above, the fast reaction process conditions allowfor the metal oxide precursor to rapidly react to a highly viscousand/or intermediate solid prior to substantial oxidation to the metaloxide coating. The process conditions allow for the association of thisintermediate metal oxide and/or interactant component form and reducesthe volatilization and/or oxidation of the metal oxide precursor off ofthe substrate. Typical powder metal oxide precursors are stannouschloride, stannous oxide, low molecular weight organic salts orcomplexes of tin, particularly low molecular weight organic salts andcomplexes such as stannous acetate and acetylacetonate complexes of tin.

An additional component powder, such as a dopant-forming powder, can becombined with the metal oxide precursor powder. A particularly preferreddopant-forming powder for tin oxide is stannous fluoride. Further, anadditional component, such as a dopant, for example a fluoride,phosphorous, indium, or antimony component for tin oxide coatings can beincorporated during any of the reactant mixture forming steps.

Typical zinc oxide precursor powders are those that are powders atpowder/substrate contacting conditions and which are preferably at leastpart liquidous at the fast reaction oxidizing conditions in the reactionzone, preferably melting within the range of about 100° C. to about 450°C., or higher, more preferably about 250° C. to about 400° C. Typicalpowder zinc oxide precursors are zinc chloride, low molecular weightorganic salts or complexes of zinc, particularly low molecular weightorganic salts and complexes such as zinc acetate and acetylacetonatecomplexes of zinc.

An additional component powder, such as a dopant-forming powder, can becombined with the zinc oxide precursor powder. Particularly preferreddopant-forming powders are aluminum and chromium acetylacetonate,benzylate and methyl substituted benzylate, cobalt II chloride, galliumdichloride, indium mono and dichloride, stannous chloride and germaniummonoxide. Further, the above dopants or an additional component, forexample a chloride or nitrate component of aluminum or titanium, can beused.

Typical copper oxide precursor powders are those that are powders atpowder/substrate contacting conditions and which are at least partliquidous at the fast reaction oxidizing conditions in the reactionzone, preferably melting within the range of about 100° C. to about 650°C., more preferably about 435° C. to about 630° C. Typical powder copperoxide precursors are cuprous chloride, cuprous oxide low molecularweight organic salts or complexes of copper, particularly low molecularweight organic salts and complexes including poly functional/carboxyl,hydroxyl and ketone such as cuprous acetate and acetylacetonatecomplexes of copper.

An additional component powder, such as the conductivity formingadditional powders, can be combined with the copper oxide precursorpowder. The particularly preferred additional powders are yttriumchloride and/or oxide, barium carbonate and/or oxide or peroxide.

As set forth above, the copper oxide precursor powders and additionalcomponent conductivity interacting component can produce a film formingamount precursor component on the substrate, particularly distributionof the film over a substantial part of said substrate, followed byoxidation. In addition to the precursor components set forth above,nitrates, sulfates and their hydrates, as well as the hydrates of forexample chloride, can be selected and used within the processingrequirements for producing such conductive coated substrate.

Typical iron oxide precursor powders are those that are powders atpowder/substrate contacting conditions in the reaction zone and whichare at least part liquidous at the fast reaction oxidizing conditions ofthe present process, preferably melting within the range of about 300°C. to about 450° C., or higher, more preferably about 350° C. to about300° C. As set forth above, the fast reaction process conditions allowfor the metal oxide precursor to rapidly react to a highly viscousand/or intermediate solid prior to substantial oxidation to the metaloxide coating. The process conditions allow for the association of thisintermediate metal oxide and/or interactant component for which reducesthe volatilization and/or oxidation of the metal oxide precursor off ofthe substrate. Typical powder iron oxide precursors are ferric chloride,low molecular weight complexes of iron, such as poly functionality andcomplexes with carboxylic, ketone and hydroxyl functionality, such asacetylacetonate complexes of iron.

An additional component powder, such as a dopant-forming powder, can becombined with the iron oxide precursor powder. Particularly preferredinteracting-forming powders are compounds of nickel, zinc, manganese,yttrium, the rare earths, barium, calcium and silica. Further, anadditional component, such as an interacting component, for example achloride hydrate and/or nitrate hydrate and/or a di-ketone complex canbe incorporated into the reactant mixture, for example, zincacetylacetonate as a source of the metal interacting compound.

As set forth above, the metal oxide precursor, optionally including theinteracting component can be associated with the substrate as liquidslurry. For example, a liquid soluble metal chloride and/or interactingcomponent, i.e. chloride or fluoride salt or a suspension and/orprecipitated suspension, may be used. The use of liquid metal oxideprecursor and/or interacting component provides advantageous substrateassociation particularly efficient and uniform association with thesubstrate. In addition, coating material losses are reduced.

The metal oxide precursors and interacting components set forth abovewith respect to powders in general can be used also to make the liquidslurries. The preferred interacting components as set forth above withrespect to powders are also preferred for the liquid slurries. Inaddition, liquids, low melting and liquid soluble metal salts can beused advantageously for the liquid slurries.

As set forth above, it is preferred that the reaction mixture liquidslurries maximize the concentration of the substrate consistent withslurry viscosity atomization requirement in the reaction zone. Theamount of metal oxide precursor and optionally interacting componentwhich are incorporated into the slurry is generally a function of thethickness of the metal oxide coating on the substrate for the finalproduct. For example, a metal oxide coating of 50 nanometers willrequire less than a 250 nanometer metal oxide coating. Further, thesurface area of the substrate, typically a function of particle size perunit weight will effect the concentration of the metal oxide precursorand interactant. The reactant slurries contain a solvent which allowsfor the solubilization and/or precipitation of one or both of the metaloxide precursor and interactant. The preferred solvents are aqueoussolvent systems containing an alcohol such as a lower molecular weightalcohol, i.e. methanol, ethanol or isopropanol and mixtures thereof,which allow for solubilization of both the metal oxide precursor andinteractant. For example, a preferred liquid slurry which containssoluble oxide precursor and interacting component are stannous andstannic chlorides and a interacting component such as antimonytrichloride or ammonium fluoride or bifluoride. The liquid slurries inaddition can have a pH less than 7 which enhances overall solubilitysuch as through the use of hydrochloric acid.

The precipitated liquid slurry reaction mixtures can be made by forminga first soluble solution of an appropriate metal oxide precursor such asmetal chloride salts in an alcohol solution or an acidic solution suchas hydrochloric acid acidic solutions and adding such solutions slowlyat elevated temperature such as from about 50° to 90° C. to an aqueoussuspension of the substrate. The gradual addition of the oxide precursorinteractant solution generally in the presence of hydroxyl ion providesfor a slow and gradual hydrolysis and precipitation of the saltsgenerally as an hydroxide, preferably on the surfaces of the substratein a uniform layer. The precipitant slurry reactant mixture isintroduced into the reaction zone for conversion to the metal oxidecoated substrate. One of the significant advantages of the process ofthis invention using precipitant slurry reaction mixtures is that theslurry itself can be directly fed into the reaction zone withoutrequiring separation of the precipitant plus substrate, washing of thesubstrate and calcinations of sintering of the precipitant associatedsubstrate. The prior art processes typically require extensiveprocessing times in the order of many hours. The precipitant slurryreaction mixture and the precipitant process are typically undertaken athigh substrate liquid slurry concentrations without the introduction ofdeleterious contaminants. Thus it is preferred to use solvent systemswhich do not contribute deleterious contaminants to the metal oxidecoating. If a source of hydroxyl ion is used to enhance theprecipitation process it is preferred to use a source such as ammoniumhydroxide or calcium hydroxide which do not substantially interfere withthe final properties of the metal oxide film. Further, in the case ofprecipitant reaction mixtures, the precipitant substrates can befiltered, washed of extraneous ions, such as sodium or chloride, andreslurried for use as a reaction mixture. In order to control theviscosity of the liquid slurries, particularly at high substrateconcentration a dispersant or defloculant can be added to reduce and/orminimize any substrate agglomeration.

The oxide precursor and/or interacting component to be contacted withthe substrate may be present in an atomized state. As used in thiscontext, the term “atomized state” refers to both a substantiallygaseous state and a state in which the oxide precursor and/orinteracting component are present as drops or droplets and/or soliddispersion such as colloidal dispersion in for example a carrier gas,i.e., an atomized state. Liquid state oxide precursor and/or interactingcomponent may be utilized to generate such reaction mixture.

In addition to the other materials, as noted above, the reactant mixturemay also include one or more grain growth inhibitor components. Suchinhibitor component or components are present in an amount effective toinhibit grain growth in the metal oxide-containing coating. Reducinggrain growth leads to beneficial coating properties, e.g., higherelectrical conductivity, more uniform morphology, and/or greater overallstability. Among useful grain growth inhibitor components are componentswhich include at least one metal ion, in particular potassium, calcium,magnesium, silicon, zinc and mixtures thereof. These components aretypically used at a concentration in the final coating of from about0.01 to 1.0 wt % basis coating. Of course, such grain growth inhibitorcomponents should have no substantial detrimental effect on the finalproduct.

The interacting component may be deposited on the substrate separatelyfrom the oxide precursor, for example, before and/or during the oxideprecursor/substrate contacting. If the interacting component isdeposited on the substrate separately from the oxide precursor it shouldbe deposited after the oxide precursor but before oxidation to the oxidefilm, such as to form soluble and/or eutectic mixtures and/ordispersions.

Any suitable interacting component may be employed in the presentprocess. Such interacting component should provide sufficientinteracting component so that the final metal oxide coating has thedesired properties, e.g., electronic conductivity, stability, magneticproperties, etc. Care should be exercised in choosing the interactingcomponent or components for use. For example, the interacting componentshould be sufficiently compatible with, for example, the oxide precursorso that the desired metal oxide coating can be formed. Interactingcomponents which are excessively volatile (relative to oxide precursor),at the conditions employed in the present process, are not preferredsince, for example, the final coating may not be sufficiently developedwith the desired properties and/or a relatively large amount of theinteracting component or components may be lost during processing. Itmay be useful to. include one or more property altering components,e.g., boiling point depressants, in the composition containing thedopant-forming component to be contacted with the substrate. Suchproperty altering component or components are included in an amounteffective to alter one or more properties, e.g., boiling point, of theinteracting component, e.g., to improve the compatibility or reduce theincompatibility between the interacting component and oxide precursor.

Particularly useful dopants for use in the tin oxide products andprocess of this invention are anion and cation dopants, particularlyfluoride components selected from stannous fluoride, stannic fluoride,ammonium fluoride, ammonium bifluoride and mixtures thereof, antimony,indium and phosphorous, i.e. orthophosphoric acid, diammoniumorthophosphate. The preferred dopants are those that provide for optimumdopant incorporation while minimizing dopant precursor losses,particularly under the preferred process conditions as set forth herein.In addition oxides or sub-oxides can also be used, including wheredopant incorporation is accomplished during the oxidation sinteringcontacting step.

The use of a fluoride dopant is an important feature of certain aspectsof the present invention. First, it has been found that fluoride dopantscan be effectively and efficiently incorporated into the tinoxide-containing coating. In addition, such fluoride dopants act toprovide tin oxide containing coatings with good electronic propertiesreferred to above, morphology and stability.

Particularly useful dopant components for use in the zinc oxide productsand process of the present invention are selected from aluminum, cobalt,gallium, titanium, indium, tin and germanium, particularly oxide formingdopant components, as well as zinc metal forming compounds and/or theuse of such process condition which form dopant concentrations of zincmetal. Preferred dopant oxide precursors are set for above and includethe halide, preferably the chlorides, organic complexes, such as lowmolecular weight organic acid salts, complexes, such as low molecularweight, ketone components, preferably 2, 4, dienes, benzylates and thelike. The preferred dopants are those that provide for optimum dopantoxide incorporation while minimizing dopant precursor losses,particularly under the preferred process condition as set forth herein.Oxides or suboxides can also be used where dopant incorporation isaccomplished during the oxidation sintering contacting step.

The use of a dopant is an important feature of certain aspects of thepresent invention. First, it has been found that such dopants,particularly aluminum can be effectively and efficiently incorporatedinto the zinc oxide-containing coating. In addition, such dopants act toprovide zinc oxide-containing coatings with good electronic propertiesreferred to above, morphology and stability.

As set forth above, the reaction zone gas phase constituents can beadjusted to provide a reducing environment after the oxidationconditions within the reaction zone. Further, the reducing conditionscan be at the tail end of the zone prior to the metal oxide coatedparticle substrates undergoing reaction quench and significantly lowertemperatures. The use of the combination of controlled oxidation andreduction zones within the reaction zone and tail portion of thereaction zone can be particularly beneficial for creating defectstructure with or without an interacting component for conductive zincoxide coated substrates.

Any suitable conductivity compatible and/or enhancing component may beemployed in the copper oxide product and processes of this invention.Such conductivity interacting component should provide sufficientstoichiometry so that the final copper oxide coating has the desiredproperties, e.g., electronic conductivity, stability, etc. Chloride,nitrate, sulfate, organic complexes as set forth above and their hydratecomponents are particularly useful additional components with oxide,peroxide and carbonates being also useful. Care should be exercised inchoosing the additional component or components for use. For example,the components should be sufficiently compatible with oxide precursorsuch as cuprous chloride so that the desired conductive copper oxidecoating can be formed.

The use of an additional component is an important feature of certainaspects of the present invention. First, it has been found that suchcomponents can be effectively and efficiently incorporated into thecopper oxide-containing coating. In addition, such additional componentsact to provide copper oxide-containing coatings with excellentelectronic properties referred to above, morphology and stability.

Any suitable interacting-forming component may be employed in the ironoxide products and processes of this invention. Such interactant formingcomponent should provide a sufficient concentration so that the finaliron oxide coating has the desired properties, e.g., magnetic, highpermeability, stability, for example, nickel, manganese or zinccomponents. Preferred iron component oxide precursors are set for aboveand include the halide, preferably the chlorides, organic complexes,such as low molecular poly functional organic acids, complexes, such aslow molecular weight, ketone components, preferably 2, 4, ketones,benzylates and the like. The preferred interacting components are thosethat provide for optimum oxide incorporation while minimizing dopantprecursor losses, particularly under the preferred process condition asset forth herein. Oxides or suboxides can also be used where dopantincorporation is accomplished during the oxidation sintering contactingstep.

The use of an interactant component is an important feature of certainaspects of the present invention. First, it has been found thatinteractant components can be effectively and efficiently incorporatedinto the iron oxide-containing coating. In addition, such interactantcomponents act to provide iron oxide-containing coatings with goodmagnetic properties referred to above, morphology and stability.

The liquid compositions, which include oxide precursor preferably alsoinclude the interactant component. In this embodiment, the interactantcomponent or components are preferably soluble and/or dispersedhomogeneously and/or atomizeable as part of the reactant mixture. Suchmixtures are particularly effective since the amount of interactantcomponent in the final metal oxide coating can be controlled bycontrolling the concentration in the reactant mixture. In addition, boththe oxide precursor and interactant component are associated with thesubstrate in one step.

If stannous fluoride and/or stannic fluoride are used in tin oxidecoatings, such fluorine components provide the dopant and are convertedto tin oxide during the oxidizing agent/reaction mixture contactingstep. This enhances the overall utilization of the coating components inthe present process. Particularly useful compositions comprise about 50%to about 98%, more preferably about 70% to about 95%, by weight ofstannous chloride and about 2% to about 50%, more preferably about 5% toabout 30%, by weight of fluoride component, in particular stannousfluoride.

In addition, if zinc chlorides are used, such chloride components canprovide the dopant and are converted to oxides during the oxidizingagent/reactant mixture contacting step. This enhances the overallutilization of the coating components in the present process.Particularly useful final zinc oxide compositions comprise about 0.1% toabout 5%, more preferably about 0.5% to about 3%, by weight of dopant.

In addition, if cuprous chloride and yttrium chloride, and a bariumoxide precursor (dispersed) are used, such components provide theconductivity stoichiometry and are converted to copper oxide during theoxidizing agent/reactant mixture contacting step. This enhances theoverall utilization of the coating components in the present process.Particularly useful compositions produce a yttrium to barium to copperoxide ratio of 1, 2, 3 or 1, 2, 4.

A preferred class of superconductor coatings are the 1, 2, 3 and 1, 2, 4superconductors of yttrium, barium and copper. In addition, thallium,barium, calcium and copper oxide in an atomic weight ratio of about 2,2, 2, 3 are also preferred. Bismuth based copper oxide conductors arefurther examples of conductors within the scope of this invention. Thecoating prepared by the process of this invention enhance the currentcarrying capability of the conductors, can reduce grain boundary currentcarring effects or provide improved control of oxidation and/orannealing conditions and uniformity, including the requisite atomicweight stoichiometry.

In addition, if chlorides or organic precursors of iron are used, suchprecursor components are converted to oxides during the oxidizingagent/reaction mixture contacting step. This enhances the overallutilization of the coating components in the present process.

The substrate including the oxide precursor and optionally theinteractant is contacted with an oxidizing agent at conditions effectiveto convert oxide precursor to metal oxide, and preferably to form aconductive and/or ferro magnetic tin oxide and/or other coating on atleast a portion of the substrate. Water, e.g., in the form of acontrolled amount of humidity, is preferably present during theoxidizing agent contacting. This is in contrast with certain prior metaloxide coating methods which are conducted under anhydrous conditions.The presence of water during this contacting has been found to providean oxide coating having excellent electrical properties particularlyconductivity.

Any suitable oxidizing agent may be employed, provided that such agentfunctions as described herein. Preferably, the oxidizing agent (ormixtures of such agents) is substantially gaseous at the reactantmixture/oxidizing agent contacting conditions. The oxidizing agentpreferably includes reducible oxygen, i.e., oxygen which is reduced inoxidation state as a result of the coated substrate/oxidizing agentcontacting. More preferably, the oxidizing agent comprises molecularoxygen, singlet oxygen either alone or as a component of a gaseousmixture, e.g., air. As set forth above, it is preferred that water vaporbe present in the reaction zone with the oxidizing agent. It has beenfound that the presence of water vapor enhances the overall oxidationhydrolysis reactions in the reaction zone and in addition can providefor improved oxidation and crystalline metal oxide containing coatingson the particle substrates.

The substrate may be composed of at least a part of any suitableinorganic material and may be in any suitable form. By the term suitableinorganic substrate is meant that the majority of the external surfaceof the particle substrate be inorganic, more preferably greater thanabout 75% and still more preferably greater than about 95% of thesurface being inorganic. The internal core of the particle substratescan be organic, preferably organic polymers having high temperaturethermal stability under the fast reaction temperature conditions in thereaction zone. The polymers can be thermoplastics or thermosets,preferably high temperature thermoplastics such as polyimides,polyamide-imides, polyetherimides, bismalemides, fluoroplastics such aspolytetrafluoroethylene, ketone-based resins, polyphenylene sulfide,polybenzimidazole, aromatic polyesters, and liquid crystal polymers.Most preferred are imidized aromatic polyimide polymers,para-oxybenzoylhomopolyester and poly(para-oxybenzoylmethyl) ester. Inaddition polyolefines, particularly crystalline high molecular weighttypes can be used. The inorganic organic substrates can be prepared byprecoating the organic substrate with an inorganic precoat as set forthbelow.

Preferably, the substrate is such so as to minimize or substantiallyeliminate deleterious substrate, coating reactions and/or the migrationof ions and other species, particularly p-dopant type cations such asalkalai metal ion, if any, from the substrate to the metaloxide-containing coating which are deleterious to the functioning orperformance of the coated substrate in a particular application.However, controlled substrate reaction which provides the requisitestoichiometry can be used and such process is within the scope of thisinvention. In addition, the substrate can be precoated to minimize ionmigration, for example an alumina and/or a silica including a silicateprecoat and/or to improve wetability and uniform distribution of thecoating materials on the substrate. The precoats can comprise one ormore members of a group of alumina, zirconium oxide, silica and otheroxides such as tin oxide. The precoats can be deposited on thesubstrates including inorganic and organic core substrates using anysuitable technique such as hydrolysis and precipitation of a solublesalt. In addition, the precoat process can be repeated in order toobtain a precoat thickness to for example minimize deleterious effectsfrom cations contained in the substrate and/or improve the thermalbarrier properties of the precoat in relationship to an organic core.The techniques for forming the precoat in general are similar to thoseset forth above for performing the precipitated liquid slurries andinclude precoat precursors to the final oxide precoat.

In addition to the above techniques for forming a precoat, the substrateparticles, particularly the inorganic particles, can be processed inaccordance with the process of this invention with a precoat formingmaterial such as silicic acid or disilicic acid. In general, the precoatprecursor would be combined with the substrate to form a precoatreaction mixture which is then subjected to process conditions in thereaction zone in order to obtain decomposition of the precursor precoatcomponent on the substrate. It is contemplated within the scope of thisinvention that a multi stage process can be used, i.e. the first stagebeing a precoat of the substrate in the reaction zone using the varioustypes of feeds similar to those set forth above which contain the metaloxide precursor and subjecting such feed to fast reaction elevatedtemperature conditions in a reaction zone to form the precoatedsubstrate. The precoated substrate can be combined with the metal oxideprecursor to be process and according to the process of this invention.

It has also been found that the substrate itself can be selectivelymelted at the surface to produce a precoat barrier layer, preferably amelt/resolidification coating, still more preferably a majority or evengreater crystalline layer on the outer surface of the inorganicsubstrate. The selective melting of the surface of the inorganicsubstrate can provide both barrier properties as well as enhancedbondability of the metal oxide coating on the substrate, particularlywith the formation of crystalline type surface coating as set forthabove. The process for the selective melting of the surface of theinorganic substrate can be done in multiple process steps or in a singlestep in carrying out the process of this invention. For example, theselective melting of the external surface of the inorganic substrate canbe done in a manner similar to the formation of a barrier coat as setforth above followed by incorporating the surface modified substratealong with the metal oxide precursor to form the reactant mixture. Thereaction mixture is then processed according to the process of thisinvention. In addition the reactant mixture can be introduced into thereaction zone under conditions wherein the selective melting andresolidification of the surface of the inorganic substrate takes place,i.e. a single step process. It has been found that the inorganicsubstrate having a surface that has undergone selective melting,resolidification has unique properties when associated with the metaloxide coating. These improved properties can include enhanced barrierproperties, bonding with the metal oxide coating and overall morphologystability.

In order to provide for controlled electrical conductivity in theconductive metal oxide coatings, it is preferred that the substrate besubstantially non-electronically conductive and/or non-deleteriousreactive and/or substantial non-magnetic when the coated substrate is tobe used as a component/such as additive of an electric/electronicdevice, acoustic device and/or magnetic device. The substrate can bepartially or completely inorganic, for example mineral, glass, ceramicand/or carbon. Examples of three dimensional substrates which can becoated using the present process include spheres, extrudates, flakes,fibers, aggregates, porous substrates, stars, irregularly shapedparticles, tubes, such as having an average largest dimension of fromabout 0.05 microns to. about 250 microns, more preferably from about 1micron to about 75 microns.

A particularly unique embodiment of the present metal oxide coatedparticles is the ability to design a particular density for a substratethrough the use of one or more open or closed cells, including micro andmacro pores particularly, including cell voids in spheres which spheresare hereinafter referred to as hollow spheres. Thus such densities canbe designed to be compatible and synergistic with other components usedin a given application, particularly optimized for compatibility inliquid systems such as polymer film coating and composite compositions.The average particle density can vary over a wide range such asdensities of from about 0.1 g/cc to about 2.00 g/cc, more preferablyfrom about 0.13 g/cc to about 1.5 g/cc, and still more preferably fromabout 0.15 g/cc to about 0.80 g/cc.

A further unique embodiment of the present invention is the ability toselectively have a metal oxide on the outer surface area while limitingthe metal oxide coating on the internal pore surface area of thesubstrate typically limiting the coating to at least about 10% noncoatedinternal pore surface area as a percentage of the total surface area ofthe substrate. Typically, the porous substrates will have a totalsurface area in the range of from about 0.01 to about 700 m²/gram ofsubstrate, more typically from about 1 to about 100 m²/gram ofsubstrate. Depending on the application such as for catalysts, thesurface area may vary from about 10 to about 600 m²/gram of substrate.

As set forth above, porous substrate particles can be in many forms andshapes, especially shapes which are not flat surfaces, i.e., nonline-of-site materials such as pellets, fiber like, beads, includingspheres, flakes, aggregates, and the like. The percent apparentporosity, i.e., the volume of open pores expressed as a percentage ofthe external volume can vary over a wide range and in general, can varyfrom about 20% to about 92%, more preferably, from about 40% to about90%. A particularly unique porous substrate is diatomite, a sedimentaryrock composed of skeletal remains of single cell aquatic plants calleddiatoms typically comprising a major amount of silica. Diatoms areunicellular plants of microscopic size. There are many varieties thatlive in both fresh water and salt water. The diatom extracts amorphoussilica from the water building for itself what amounts to a strong shellwith highly symmetrical perforations. Typically the cell walls exhibitlacework patterns of chambers and partitions, plates and apertures ofgreat variety and complexity offering a wide selection of shapes. Sincethe total thickness of the cell wall is in the micron range, it resultsin an internal structure that is highly porous on a microscopic scale.Further, the actual solid portion of the substrate occupies only fromabout 10-30% of the apparent volume leaving a highly porous material foraccess to liquid. The mean pore size diameter can vary over a wide rangeand includes macroporosity of from about 0.075 microns to 10 micronswith typical micron size ranges being from about 0.5 microns to 15 about5 microns. As set forth above, the diatomite is generally amorphous andcan develop crystalline character during calcination treatment of thediatomite. For purposes of this invention, diatomite as produced orafter subject to treatment such as calcination are included within theterm diatomite.

The particularly preferred macroporous particles for use in thisinvention are diatomites obtained from fresh water and which havefiber-like type geometry. By the term fiber-like type geometry is meantthat the length of the diatomite is greater than the diameter of thediatomite and in view appears to be generally cylindrical and/orfiber-like. It has been found that these fiber-like fresh waterdiatomites provide improved properties in coatings and compositeapplications.

As set forth above, substrates can be inorganic for example, carbonincluding graphite and/or an inorganic oxide. Typical examples ofinorganic oxides which are useful as substrates include for example,substrates containing one or more silicate, aluminosilicate, silica,sodium borosilicate, insoluble glass, soda lime glass, soda limeborosilicate glass, silica alumina, titanium dioxide, mica, as wellother such glasses, ceramics and minerals which are modified with, forexample, another oxide such as titanium dioxide and/or small amounts ofiron oxide.

Additional examples of substrates are wollastonite, titanates, such aspotassium hexa and octa titanate, carbonates and sulfates of calcium andbarium; borates such as aluminum borate, a natural occurring quartz andvarious inorganic silicates, clays, pyrophyllite and other relatedsilicates.

A particularly unique coated three-dimensional substrate is a flakeand/or fiber particle, such as having an average largest dimension, i.e.length of from about 0.1 micron to about 200 microns more preferablyfrom about 1 micron to about 100 microns, and still more preferably fromabout 5 microns to about 75 microns, particularly wherein the aspectratio, i.e., the average particle length divided by the thickness of theparticle is from about five to one to about 200 to 1, more preferablyfrom about 25 to 1 to about 200 to 1 and still more preferably, fromabout 50 to 1 to about 200 to 1. Generally, the particles will have athickness varying from about 0.1 microns to about 15 microns, morepreferably from about 0.1 micron to about 10 microns. The averagelength, i.e., the average of the average length plus average width ofthe particle, i.e., flake, will generally be within the aspect ratios asset forth above for a given thickness. Thus for example the averagelength as defined above can from about 1 micron to about 300 microns,more typically from about 20 microns to about 150 microns. In general,the average length can vary according to the type of substrate and themethod used to produce the platelet material.

For example, C glass in general has an average length which can varyfrom about 20 microns up to about 300 microns, typical thicknesses offrom about 1.5 to about 15 microns. Other particle materials forexample, hydrous aluminum silicate mica, in general can vary in lengthfrom about 5 to about 100 microns at typical thicknesses or from about0.1 to about 7.0 microns, preferably within the aspect ratios set forthabove. In practice the particles which are preferred for use in suchapplications in general have an average length less than about 300microns and an average thickness of from about 0.1 to about 15 microns.Ceramic fibers are particularly useful substrates when the copper oxidecoated substrate is to be used as a superconductor.

A particular unique advance in new products resulting from the processof this invention are the production of metal oxide coated nano particlesubstrates typically having an average particle size less than 1,000nanometers, typically less than 500 and still typically less than 100nanometers. In many applications the average particle size will be lessthan about 50 nanometers. The particle size distribution of the nanoparticle substrates are skewed towards the smaller particle size andtypically have greater than 90%, often greater than 95% of the totalnumber particles on a weight basis, less than 1,000 nanometers,typically less than 500 nanometers, and still more typically less than100 nanometers. It has been discovered that the use of liquid slurryreaction mixtures particularly metal oxide precursor and optionallyinteracting component which are soluble in the slurry liquid are able toproduce metal oxide coated nanosubstrates which vary in thickness fromabout 5% to about 75%, more preferably from about 10% to about 60% ofthe average thickness on the smallest dimension of the substrateparticle, such as the thickness in a flake or the diameter in a fiber.The various physical and chemical properties of the substrates andcoatings as set forth above are applicable to nanosubstrates. Thesignificant advantage of the soluble metal oxide precursor and/orinteracting component is the ability to provide the concentration ofthese coating forming components that produce the desired coatingthickness on the nanosubstrates.

A particular unique substrate is referred to as swelling clays orsmectites. These types of clays have a layered structure where in eachlayer can be treated to expand the spacing between layers such as toprovide individual layers of the clay of vary small thicknesses such asfrom about 1 to 2 nanometers. The aspect ratios are significantparticularly if the largest length extends to 1,000 nanometers. Thespacing between the different sheets are called the gallery which areexpanded upon treatment particularly with polar materials to provide forincreased spacing between each sheet.

These phyllosilicates, such as smectite clays, e.g., sodiummontmorillonite and calcium montmorillonite, can be treated with polarmolecules, such as ammonium ions, to intercalate the molecules betweenadjacent, planar silicate layers, for intercalation of precursor betweenthe layers, thereby substantially increasing the interlayer(interlaminar) spacing between the adjacent silicate layers. Thethus-treated, interclalted phyllosilicates, having interlayer spacingsof at least about 10-20. ANG. and up to about 100 .ANG., then can beexfoliated, e.g., the silicate layers are separated, e.g., mechanically,by high shear mixing. The individual layers have been found tosubstantially improve one or more properties of polymer coatings andcomposites, such as mechanical strength and/or high temperaturecharacteristics.

Useful swellable layered materials include phyllosilicates, such assmectite clay minerals, e.g., montmorillonite, particularly sodiummontmorillonite; magnesium montmorillonite and/or calciummontmorillonite; nontronite; beidellite; volkonskoite; hectorite;saponite; sauconite; sobockite; stevensite; svinfordite; vermiculite;and the like. Other useful layered materials include micaceous minerals,such as illite and mixed layered illite/smectite minerals, such asrectorite, tarosiovite, ledikite and admixtures of illites with the clayminerals set forth above.

As set forth above the reaction mixture can be in a powder form with themetal oxide precursor present on the surface of the substrate as hasbeen illustrated above. The powders can be associated with the surfaceof the substrate by attraction through opposite static charges. Inaddition a binder can be associated with the metal oxide precursorpowder, which enhances the association of the precursor powder with thesubstrate. The binder can be inorganic or organic. As set forth above,the binder should not introduce any substantial deleterious contaminantsinto the metal oxide coating or substantially adversely affect theoverall film properties such as conductive or magnetic properties. Thebinders can be for example polymeric type such as polyvinylalcohol orpolyvinylpyrrolidone. In addition, the binder can have both organic andinorganic functionality such as an organic silicate such as an ethylsilicate. In addition, the inorganic binders can be used such as calciumsilicate, boric oxide and certain carbonate, nitrates and oxalates. Inthe case of organic binders it is preferred to use such organic bindersthat will be converted to a carbon oxide such as carbon monoxide orcarbon dioxide under the process conditions in the reaction zone withoutleaving any substantial deleterious carbon contaminant associated withthe metal oxide coated substrate. In addition, the use of organicbinders can provide for a reducing atmosphere in a transition fromoxidizing conditions to reducing conditions in the reactor zone or theexit of the reactor zone. It is preferred to use a binderless powdersubstrate reaction mixture in order to eliminate potential contaminanteffects. When a binder is used, the concentration of the binder is suchas to maintain the individual particle substrate integrity or ifagglomeration does occur, to be easily converted to nonagglomeratedparticles through low severity mechanical processing such as ballmilling.

The coated particles are particularly useful in a number ofapplications, particularly lead acid batteries, including conductivityadditives for positive active material, catalysts, heating elements,electrostatic dissipation elements, electromagnetic interferenceshielding elements, electrostatic bleed elements, protective coatings,field dependent fluids, laser marking and the like. In practicespherical particles for use in applications in general have a roundnessassociated with such particles, generally greater than about 70% stillmore preferably, greater than about 85% and still more preferably,greater than about 95%. The spherical products offer particularadvantages in many of such applications disclosed herein, includingenhanced dispersion and rheology, particularly in various compositionssuch as polymer compositions, coating compositions, various other liquidand solid type compositions and systems for producing various productssuch as coatings and polymer composites.

The substrate for use in lead-acid batteries is acid resistant. That is,the substrate exhibits some resistance to corrosion, erosion and/orother forms of deterioration at the conditions present, e.g., at or nearthe positive plate, or positive side of the plates, in a lead-acidbattery.

Ferrite is a generic term describing a class of magnetic oxide compoundsthat contain iron oxide as a major component. There are several crystalstructure classes of compounds broadly defined as ferrites, such asspinel, magnetoplumbite, garnet, and perovskite structures.

Although there are many characterizations specific to a givenapplication, one property is shared by all materials designed asferrites, namely the existence of a spontaneous magnetization (amagnetic induction in the absence of an external magnetic field).

Any suitable matrix material or materials may be used in a compositewith the metal oxide coated substrate. Preferably, the matrix materialcomprises a polymeric material, e.g., one or more synthetic polymers,more preferably an organic polymeric material. The polymeric materialmay be either a thermoplastic material or a thermoset material. Amongthe thermoplastics useful in the present invention are the polyolefins,such as polyethylene, polypropylene, polymethylpentene and mixturesthereof; and poly vinyl polymers, such as polystyrene, polyvinylidenedifluoride, combinations of polyphenylene oxide and polystyrene, andmixtures thereof. Among the thermoset polymers useful in the presentinvention are epoxies, phenol-formaldehyde polymers, polyesters,polyvinyl esters, polyurethanes, melamine-formaldehyde polymers, andurea-formaldehyde polymers.

In yet another embodiment, a metal oxide coated substrate includingtransition and tin metal oxide, preferably electronically conductivemetal oxide, and optionally at least one additional catalyst componentcan be used as catalysts in an amount effective to promote a chemicalreaction. Preferably, the additional catalyst component is a metaland/or a component of a metal effective to promote the chemicalreaction. A particularly useful class of chemical reactions are thoseinvolving chemical oxidation or reduction. For example, an especiallyuseful and novel chemical reduction includes the chemical reduction ofnitrogen oxides, to minimize air pollution, with a reducing gas such ascarbon monoxide, hydrogen and mixtures thereof. A particularly usefulchemical oxidation application is a combustion, particularly catalyticcombustion, wherein the oxidizable compounds, i.e., carbon monoxide andhydrocarbons are combusted to carbon dioxide and water. For example,catalytic converters are used for the control of exhaust gases frominternal combustion engines and are used to reduce carbon monoxide andhydrocarbons from such engines. Of course, other chemical reactions,e.g., oxidative coupling of methane to alkanes and alkenes, hydrocarbonreforming, dehydrogenation, such as alkylaromatics to olefins, olefinsto dienes, alcohols to ketones hydrodecyclization, isomerization,ammoxidation, such as with olefins, aldol condensations using aldehydesand carboxylic acids and the like, may be promoted using the presentcatalysts.

Any suitable additional catalyst component (or sensing component) may beemployed, provided that it functions as described herein. Among theuseful metal catalytic components and metal sensing components are thoseselected from components of the tins, the rare earth metals, certainother catalytic components and mixtures thereof, in particular catalystscontaining gold, silver, copper, vanadium, chromium, cobalt molybdenum,tungsten, zinc, indium, the platinum group metals, i.e., platinum,palladium and rhodium, iron, nickel, manganese, cesium, titanium, etc.Although metal containing compounds may be employed, it is preferredthat the metal catalyst component (and/or metal sensing component)included with the metal oxide coated substrates comprise elemental metaland/or metal in one or more active oxidized forms, for example, Cr₂O₃,Ag₂O, etc.

The preferred substrate materials for catalysts include a wide varietyof materials used to support catalytic species, particularly porousrefractory inorganic oxides. These supports include, for example,alumina, silica, zirconia, magnesia, boria, phosphate, titania, ceria,thoria and the like, as well as multi-oxide type supports such asalumina-phosphorous oxide, silica alumina, zeolite modified inorganicoxides, e.g., silica alumina, and the like. As set forth above, supportmaterials can be in many forms and shapes, especially porous shapeswhich are not flat surfaces. The catalyst materials can be used as is orfurther processed such as by sintering of powered catalyst materialsinto larger aggregates. The aggregates can incorporate other powders,for example, other oxides, to form the aggregates.

A particularly unique property of the ferro magnetic products of thisinvention is the ability to be able to separate and recover catalystsfrom solution and/or other non-magnetic or low permeability solids bymagnetic separation. This is particularly advantageous in slurrycatalysts, such as in liquid systems, such as hydrocarbon and/or aqueousand/or combination systems. This property allows separation includingseparation from other non-magnetic solids and separate catalystregeneration if required.

In addition, the ability to vary coating thickness and substratecomposition allows designing catalyst for a given density, a featureimportant in gravity separation processes.

The metal oxide coated/substrate of the present invention are useful inother applications as well. Among these other applications are includedporous membranes, heating elements, electrostatic dissipation elements,electromagnetic interference shielding elements, protective coatings,field dependent fluids and the like.

In another embodiment, the porous membrane comprises a porous organicmatrix material, e.g., a porous polymeric matrix material, and a metaloxide-containing material in contact with at least a portion of theporous organic matrix material. With the organic matrix material, themetal oxide-containing material may be present in the form of a porousinorganic substrate, having a metal oxide-containing coating, e.g., anelectronically conductive and/or ferro magnetic metal oxide-containingcoating, thereon.

In addition, an electrostatic dissipation/electromagnetic interferenceshielding element is provided which comprises a three dimensionalsubstrate, e.g., an inorganic substrate, having an electricallyconductive and/or ferromagnetic transition metal oxide-containingcoating on at least a portion of all three dimensions thereof. Thecoated substrate is adapted and structured to provide at least one ofthe following: electrostatic dissipation and/or bleed andelectromagnetic interference shielding.

A very useful application for the products of this invention is forstatic, for example, electrostatic, dissipation and shielding,particularly for polymeric parts, and more particularly as a means foreffecting static dissipation including controlled static discharge anddissipation such as used in certain electro static painting processesand/or electric field absorption in parts, such as parts made ofpolymers and the like, as described herein. The present products can beincorporated directly into the polymer or a carrier such as a cured oruncured polymer based carrier or other liquid, as for example in theform of a liquid, paste, hot melt, film and the like. Theseproduct/carrier based materials can be directly applied to parts to betreated to improve overall performance effectiveness. A heating cycle isgenerally used to provide for product bonding to the parts. Aparticularly unexpected advantage is the improved mechanical properties,especially compared to metallic additives which may compromisemechanical properties. In addition, the products of this invention canbe used in molding processes to allow for enhanced static dissipationand/or shielding properties of polymeric resins relative to an articleor device or part without such product or products, and/or to have apreferential distribution of the product or products at the surface ofthe part for greater volume effectiveness within the part.

The particular form of the products, i.e., fibers, flakes, irregularlyshaped and/or porous particles, or the like, is chosen based upon theparticular requirements of the part and its application, with one ormore of flakes, fibers and particles, including spheres, being preferredfor polymeric parts. In general, it is preferred that the products ofthe invention have a largest dimension, for example, the length of fiberor particle or side of a flake, of less than about 300 microns, morepreferably less than about 150 microns and still more preferably lessthan about 100 microns. It is preferred that the ratio of the longestdimension, for example, length, side or diameter, to the shortestdimension of the products of the present invention be in the range ofabout 500 to 1 to about 10 to 1, more preferably about 250 to 1 to about25 to 1. The concentration of such product or products in theproduct/carrier and/or mix is preferably less than about 60 weight %,more preferably less than about 40 weight %, and still more preferablyless than about 20 weight %. A particularly useful concentration is thatwhich provides the desired performance while minimizing theconcentration of product in the final article, device or part.

The products of this invention find particular advantage in staticdissipation parts, for example, parts having a surface resistivity inthe range of about 10⁴ ohms/square to about 10¹² ohms/square. Inaddition, those parts generally requiring shielding to a surfaceresistivity in the range of about 1 ohm/square to about 10⁵ ohms/squareand higher find a significant advantage for the above products due totheir mechanical properties and overall improved polymer compatibility,for example, matrix bonding properties as compared to difficult to bondmetal and carbon-based materials. A further advantage of the aboveproducts is their ability to provide static dissipation and/or shieldingin adverse environments such as in corrosive water and/or electrogalvanic environments. As noted above, the products have the ability toabsorb as well as to reflect electro fields. The unique ability of theproducts to absorb allows parts to be designed which can minimize theamount of reflected electro fields that is given off by the part. Thislatter property is particularly important where the reflected fields canadversely affect performance of the part.

In addition to the above described applications, zinc oxide isparticularly useful in applications which require a large electromechanical coupling coefficient, such as transducers in surface acousticwave devices and microwave delay lines and various other acoustic andpiezo devices. Such properties also have applications in telephoneequipment, strain gauges, acoustic optical devices, i.e., laserdeflectors and Fourier transform devices.

The potential applications for superconducting materials includelarge-scale, passive application such as shields or waveguides,superconductors screen or reflect electromagnetic radiation and usesrange from coatings on microwave cavities to shielding againstelectromagnetic pulses and bearings. Repulsive forces of superconductorsexcluding magnetic fields provide for noncontact bearings.

In addition, high-current, high-field, applications include magneticimaging/scientific equipment, such as, Superconducting magnets fornuclear magnetic resonance and imaging spectrometers and particleaccelerators; Magnetic separation, such as, magnets used for separationand purification of steel scrap, clays, ore streams, stack gases, anddesulfurizing coal.

Magnetic levitation such as high-speed train systems; electromagneticlaunch systems which can accelerate objects at high velocity. Possibleuses include rapidly repeatable, i.e., earth satellite launching,aircraft catapults, and small guns for military uses.

Other magnet applications include powerful magnets in compactsynchrotrons for electronic thin-film lithography, crystal growth,magnetohydrodynamic energy conversion systems, and ship propulsion bysuperconducting motors or by electromagnetic fields. Other high currenthigh field applications include electric power transmission, such as,transmission cables, carrying more current than conventional conductorswithout loss. Such conductors must be mechanically rugged and operateunder high field and high current conditions; energy storage, such as,large superconducting magnetic coils buried in the ground that can storevast amounts of electrical energy, without power loss, in persistent,circulating currents; load leveling for utilities and as power sourcesfor military systems such as pulsed lasers; generators and motors, suchas, low-temperature system operating with liquid helium. Motors can beused in ship propulsion, railway engines, and helicopters.

In the area of electronics, applications include passive devices, suchas, high-speed wire interconnects in electronic circuits, digitaldevises, such as, superconducting components, based on Josephsonjunctions, to be used as switches or in computer logic and memory. Inaddition, the potential for hybridized semiconductor/superconductorelectronic devices may provide yet unknown applications and devices;sensors, such as, superconducting quantum interference devices, SQUIDs)made from Josephson junctions which are extremely sensitive detectors ofelectromagnetic signals. Low-temperature SQUIDs are used in biomedical,geophysical, and submarine or airplane detection, infrared and microwavesensors.

Other devices include analog-to-digital convertors, voltage standards,signal processors, microwave mixers, filters, and amplifiers.

The copper oxide coated substrate, such as the 1, 2, 3 and 1, 2, 4copper oxide coated substrate, of the present invention may be, forexample, a component itself or a component of a composite together withone or more matrix materials. The composites may be such that the matrixmaterial or materials substantially totally encapsulate or surround thecoated substrate, or a portion of the coated substrate may extend awayfrom the matrix material or materials.

The iron oxide/substrate combinations, including Fe₃O₄, e.g., the ironoxide coated substrates, of the present invention are useful in otherapplications as well.

The applications for the spinel ferrites can be grouped into severalmain categories: main cores, and linear, power, and recording-headapplications.

Magnetic-core memories are based on switching small turoidal cores ofspinel ferrite between two stable magnetic states. Such core memoriesare used in applications where ruggedness and reliability are necessary,e.g., military applications.

The linear or low signal applications are those in which the magneticfield in the ferrite is well below the saturation level and the relativemagnetic permeability can be considered constant over the operatingconditions.

The manganese-zinc-ferrite materials characteristically have higherrelative permeabilities, higher saturation magnetization, lower losses,and lower resistivities. Since the ferromagnetic resonance frequency isdirectly related to the permeability the usual area of application isbelow 2 MHz.

At low signal levels, ferrite cores are used as transformers, lowfrequency and pulse transformers, or low energy inductors. As inductors,the manganese-zinc-ferrites find numerous applications in the design oftelecommunications equipments where they must provide a specificinductance over specific frequency and temperature ranges.Nickel-zinc-ferrites with lower saturation magnetization, generallylower relative magnetic permeabilities, and lower resistivities(10⁶·Cm), produce ferromagnetic resonance effects at much higherfrequencies than the manganese-zinc-ferrites. They find particularapplication at frequencies from 1 to 70 MHz (46).

By adjustment of the nickel-zinc ratio it is possible to prepare aseries of materials covering the relative permeability range of 10-2000.These rods, high frequency power transformers, and pulse transformers. Avariety of materials have been developed to serve these applications.

The lower magnetic losses of ferrite materials and its higher resistance(10 ohm.cm) compared with laminated transformer steel permits ferritecores to be used as the transformer element in high frequency powersupplies. Commonly known as switched-mode power supplies, they operateat a frequency of 15-30 kHz and offer higher efficiencies and smallersize than comparable laminated steel transformers.

Television and audio applications include yoke rings for the deflectioncoils for television picture tubes, flyback transformers, and variousconvergence and pincushion intortion corrections, as well as antennarods.

Manganese-zinc and nickel-zinc-spinel ferrites are used in magneticrecording heads for duplicating magnetic tapes and the recording ofdigital information. Most recording heads are fabricated frompolycrystalline nickel-zinc-ferrite for operating frequencies of 100 kHzto 2.5 GHz.

The unique properties of hexagonal ferrites are low density, and highcoercive force.

The ceramic magnet can be used in d-c permanent magnet motors,especially in automotive applications, such window life, flower, andwindshield-wiper motors.

Other grades of barium and strontium ferrite material have beendeveloped for similar applications.

Other applications of hexagonal ferrites are used in self-resonantisolators where the strong magnetocrystalline anisotropy permits aresonator without laded-c magnetic biasing fields.

Hexagonal ferrites are also used as magnetic biasing components inmagnetic bubble memories.

EXAMPLE 1

A liquid slurry reaction mixture is formed from a silica platelet havingan average particle size of about 50 microns, stannic chloride, antimonytrichloride (15 mole %), water and methanol. The substrate is at aconcentration of about 45 wt % basis the total weight of the reactionmixture. The tin and antimony chloride are soluble in the reactionmixture.

The reaction mixture is fed into a reaction zone at elevatedtemperature. The elevated temperature is maintained by an RF inductionplasma system operating at a power of about 30 kW at a frequency of 3MHz. The central swirl gas is argon and the sheath gas, a mixture ofargon and oxygen. The carrier gas is air. The reaction mixture isintroduced into the reaction zone at a flow rate of 7.5 grams perminute. The gas velocities in the reaction zone are controlled to allowfor an average particle residence time of about 15 milliseconds. Thetemperature within the reaction zone is controlled to allow for thestructural solid maintenance of the substrate. The introduction of thereaction mixture is assisted by the air atomization of the reactionmixture. Tin oxide, antimony doped coated silica substrates arerecovered in a collection zone. The collection zone uses a fabric bagfilter to remove and recover the metal oxide coated substrates.

EXAMPLE 2

Example 1 is repeated except that the alcohol is removed from thereaction mixture and hydroxide ion is slowly added to the solution toprovide for precipitation of tin and antimony metal salts on thesubstrate. A tin oxide coated silica substrate is recovered in thecollection chamber.

EXAMPLE 3

Example 1 is repeated except that a flame combustion thermal source isused in place of the RF induction plasma system. In place of thecentral, sheath and carrier gases, a combustion gas having approximately4 mole % oxygen was generated using air, propane and added water vapor.The average particle substrate residence time in the reaction zone wasten milliseconds. A tin oxide coated silica substrate is recovered.

EXAMPLE 4

Example 1 is repeated except that the reaction mixture is a free flowingpowder obtained from contacting the silica platelet substrate with ananhydrous stannous chloride and stannous fluoride (25 mole %) having anaverage particle size of 5 microns. The central gas is argon enrichedwith water vapor, the sheath gas is air argon and the carrier gas isair. The reaction mixture is introduced at a rate of about 6 grams perminute. The average velocity of the particle substrate is 5 meters persecond. A tin dioxide (antimony doped) silica platelet is recovered.

EXAMPLE 5

Example 4 is repeated except that water vapor is introduced into thesheath gas to promote formation of the crystalline doped tin dioxidecoating.

EXAMPLE 6

Example 4 is repeated except the tin and antimony chlorides are replacedby zinc chloride and aluminum nitrate. Further the amount of oxygen inthe carrier gas is reduced to a slight excess over that required foroxidation to zinc oxide and hydrogen is introduced into the sheath gasto promote the formation of a reducing atmosphere in the latter portionof the reaction zone. A zinc oxide aluminum doped coating on the silicasubstrate is recovered in the collection zone.

EXAMPLE 7

Example 1 is repeated except that the substrate is mica which isprecoated with a silica precursor to form a barrier coat. The averageparticle size of the mica is 20 microns. Antimony doped tin oxide coatedmica is recovered in the collection zone.

EXAMPLE 8

Example 7 is repeated except the mica is replaced with a polyimidepowder having an average particle size of 40 microns. The silicaprecursor is tetraethoxysilicate. An antimony doped tin oxide coatedsilica on polyimide substrate is recovered.

EXAMPLES 9 and 10

Examples 1 and 2 are repeated except that the tin and antimony chloridesare replaced by titanium tetrachloride. A titanium dioxide coated silicasubstrate having pearlescent properties is recovered in the collectionzone.

EXAMPLES 11 and 12

Examples 1 and 2 are repeated except the average particle substrateresidence time is increased to 30 milliseconds. An antimony doped tindioxide having uniform crystalline coating on the silica substrate isrecovered in the collection zone;

EXAMPLES 13 and 14

Examples 1 and 2 are repeated except that the average particle residencetime is defined by particle velocity and is about 3 meters per second.An antimony doped tin dioxide coated silica substrate is recovered inthe collection zone.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed is:
 1. An article comprising a multilayered threedimensional inorganic particle substrate having external surfaces andshielded surfaces which are at least partially shielded by otherportions of said substrate and having an inner core, a thermally meltedand resolidified external barrier surface derived from a part of saidinner core and a metal oxide coating thermally associated with saidresolidified surface, said resolidified surface and metal oxide coatingbeing on at least a portion of said same external and shielded surfacesand formed at the thermal melting conditions of the inner core surface.2. The article of claim 1 wherein the metal is selected from the groupconsisting of tin, copper, zinc, iron, chromium, tungsten, indium,molybdenum, titanium, zirconium, and mixtures thereof.
 3. The article ofclaim 2 wherein the metal is selected from the groups consisting of tin,zinc, iron, titanium and zirconium.
 4. The article of claim 1 whereinthe particle substrate is selected from the group consisting of glass,ceramic, mineral, and mixtures thereof.
 5. The article of claim 4wherein the particle substrate is selected from the group consisting ofparticle substrates which are predominant in silica, silicate, ortitanium oxide.
 6. The article of claim 4 wherein the particle substrateis in a form selected from the group consisting of spheres, flakes,fibers, porous substrates, and irregularly shaped particles.
 7. Anarticle comprising a multilayered three dimensional inorganic particlesubstrate having external surfaces and shielded surfaces which are atleast partially shielded by other portions of said substrate and havingan inner core, a thermally melted and resolidified external barriersurface derived from a part of said inner core and a metal oxideinteractant coating thermally associated with said resolidified surface,said resolidified surface and metal oxide coating being on at least aportion of said same external and shielded surfaces and formed at thethermal melting conditions of the inner core surface.
 8. The article ofclaim 7, wherein the metal is selected from the group consisting of tin,copper, zinc, iron, chromium, tungsten, indium, molybdenum, titanium,zirconium, and mixtures thereof.
 9. The article of claim 8 wherein themetal oxide and interactant are selected from the group consisting oftin metal and an interactant selected from the group consisting offluoride, antimony, and phosphorous and zinc metal and aluminuminteractant.
 10. The article of claim 7 wherein the particle substrateis selected from the group consisting of glass, ceramic, mineral, andmixtures thereof.
 11. The article of claim 8 wherein the particle isselected from the group consisting of particle substrates which arepredominant in silica, silicate, or titanium oxide.
 12. The article ofclaim 9 wherein the particle is selected from the group consisting ofparticle substrates which are predominant in silica, silicate, ortitanium oxide.
 13. The article of claim 10 wherein the particlesubstrate is in a form selected from the group consisting of spheres,flakes, fibers, porous substrates and irregularly shaped particles. 14.The article of claim 7 wherein the interactant component is present inan effective amount to modify electrical conductivity, ferromagnetic orcatalyst properties.
 15. The article of claim 8 wherein the interactantcomponent is present in an effective amount to modify electricalconductivity, ferromagnetic or catalyst properties.
 16. The article ofclaim 9 wherein the metal oxide and interactant are tin and antimony.17. The article of claim 12 wherein the metal oxide and interactant aretin and antimony.
 18. The article of claim 13 wherein the metal oxideand interactant are tin and antimony.
 19. An article comprising amultilayered three dimensional inorganic particle substrate havingexternal surfaces and shielded surfaces which are at least partiallyshielded by other portions of said substrate and having an inner core, athermally melted and resolidified poly crystalline external barriersurface derived from a part of said inner core and a metal oxideinteractant coating thermally associated with said resolidified surface,said resolidified surface and metal oxide coating being on at least aportion of said same external and shielded surfaces and formed at thethermal melting conditions of the inner core surface.
 20. The article ofclaim 19 wherein the metal is selected from the group consisting of tin,copper, zinc, iron, chromium, tungsten, indium, molybdenum, titanium,zirconium, and mixtures thereof.
 21. The article of claim 20 wherein themetal is selected from the groups consisting of tin, zinc, iron,titanium and zirconium.
 22. The article of claim 19 wherein the particlesubstrate is selected from the group consisting of glass, ceramic,mineral, and mixtures thereof.
 23. The article of claim 22 wherein theparticle substrate is selected from the group consisting of particlesubstrates which are predominant in silica, silicate, or titanium oxide.24. The article of claim 23 wherein the particle substrate is in a formselected from the group consisting of spheres, flakes, fibers, poroussubstrates, and irregularly shaped particles.
 25. The article of claim19 wherein the interactant component is present in an effective amountto modify electrical conductivity, ferromagnetic or catalyst properties.26. The article of claim 20 wherein the interactant component is presentin an effective amount to modify electrical conductivity, ferromagneticor catalyst properties.
 27. The article of claim 26 wherein the metaloxide and interactant are tin and antimony.
 28. The article of claim 26wherein the metal oxide and interactant are tin and fluoride.
 29. Thearticle of claim 22 wherein the metal oxide and interactant are tin andantimony.
 30. The article of claim 22 wherein the metal oxide andinteractant are tin and fluoride.